1. Field of the Invention
The present invention relates to a steel for shaft, and more particularly to a steel for shaft for use in the production of various shafts, for example, a shaft for paper feed, a printing head shaft and a scan head supporting shaft incorporated into office automation machines including facsimiles, printers, copying machines, and scanners, which steel is advantageous in that it need not be plated for improving the corrosion resistance, thus making it possible to reduce the cost therefor.
2. Prior Art
Recently, in accordance with the rapid spread of personal computers, demands for, for example, printers are being largely increased. Under these circumstances, the competition for the price of printers is fierce, and it is of urgent necessity to reduce the production cost for printers.
Generally, the current printers are roughly classified into ink-jet printers, such as color printers, and laser printers. These printers have incorporated thereinto a plurality of shafts including a shaft for feeding papers to be printed and a printing head supporting shaft for slidably supporting the printing head. Thus, reduction of the cost for these shafts leads to the reduction in the cost for printers.
Stainless steel, such as SUS416, is generally used in the shaft for laser printer. On the other hand, general free-cutting steel, typified by 12L14, is used in the ink-jet printers including color printers. The 12L14 has an advantage in that its cost is low; however, it poses a problem that the corrosion resistance is poor. For this reason, conventionally, the printer shaft comprised of 12L14 is generally plated with, e.g., nickel so as to impart corrosion resistance to the printer shaft.
However, in the production of such a shaft, a step for plating is required, and thus an increase in the number of steps for production causes the production cost to rise. Further, equipment for the plating step and wastewater disposal equipment inevitably necessary for plating are needed, so that the cost inevitably rises due to the cost for equipment. Furthermore, the plating treatment is not desired from a viewpoint of environmental disruption.
In view of the above, an attempt to use in the ink-jet printer stainless steel having excellent corrosion resistance, such as SUS416, which is used in the shaft for laser printer, can be considered. However, the stainless steel is expensive and therefore, the use of such stainless steel in the ink-jet printer which is of low price is further disadvantageous in the achievement of reduction in the price of the ink-jet printer.
Therefore, development of a steel for shaft, which has excellent corrosion resistance without being plated and enables the whole cost to be reduced, is desired. In addition, the shaft is required both to reduce the cost and to have excellent processability, such as machinability, and excellent straightness. Particularly, in the printing head supporting head, a considerable impact is applied to the shaft during the sliding of the printing head. Therefore, excellent straightness is an important prescribed property.
It is an object of the present invention to provide a steel for shaft, which is advantageous not only in that it has excellent corrosion resistance without being plated on its surfaces, but also in that it has excellent processability, such as machinability, and excellent straightness as well as excellent mechanical strength.
For attaining the above object, in the present invention, there is provided a steel for shaft, comprising:
0.05% by mass or less of C; 0.15% by mass or less of Si;
0.40% by mass or less of Mn; 6.0 to 10.0% by mass of Cr; 0.10% by mass or less of S; 0.30 to 0.80% by mass of Ni; 0.10 to 0.30% by mass of Pb; 0.001 to 0.10% by mass of N; and the balance of Fe and an unavoidable impurity.